| 年度 | 实际值 |
|---|---|
| 1995 | 27.6 |
| 1996 | 26.6 |
| 1997 | 24.85 |
| 1998 | 22.6 |
| 1999 | 22.6 |
| 2000 | 22.4 |
| 2001 | 22 |
| 2002 | 20.75 |
| 2003 | 20.46 |
| 2004 | 22.07 |
| 2005 | 22.89 |
| 2006 | 20.71 |
| 2007 | 21.47 |
| 2008 | 21.27 |
| 2009 | |
| 2010 | 17.34 |
| 2011 | 16.75 |
| 2012 | 16.28 |
| 2013 | 16.42 |
| 2014 | 15.67 |
| 2015 | 15.29 |
| 2016 | 15.31 |
| 2017 | |
| 2018 | 13.08 |